1. Field of the Invention
The present invention relates to sound attenuation systems that restrict airborne and structural-borne sound wave transmission; and more particularly, to an air intake manifold shell having a combination of compositional and structural features that significantly reduce engine induced noise.
2. Description of the Prior Art
Continued efforts to reduce vehicle weight and cost have led automobile manufactures to replace metal components with alternative materials. Plastic air intake manifolds represent one example of this trend. These air intake manifolds cost and weigh less thus reducing manufacturing costs while increasing fuel efficiency. Air intake manifolds currently sold to original equipment manufacturers are segregated into several feature categories. Significant feature categories typically considered include cost, temperature performance, aesthetics, recycling aspects and noise abatement performance.
While materials such as nylons have been used in air intake manifold applications, such attempts to meet automotive needs have encountered manufacturing and performance issues; there remains significant room for improvement in low cost noise abatement air intake manifolds. Because of the imminent noise radiation increase with plastic components, most engine systems require air intake manifolds or shields as a separate component. Typical materials used for acoustic shields are polyurethanes, foam and fiber pads, usually treated onto the plastic shell. These all require post injection molding operations and are therefore costly. In addition, the noise attenuation provided by such shields has been unsatisfactory.
Conventionally, noise has been reduced using air intake manifolds of the type described by increasing the surface density of the air intake manifold shell. In cases where a noise source is identified, stiffening ribs have been added, or the mass of the air intake manifold shell has been increased.
No one has taken the approach of incorporating the noise shielding function into the plastic component itself, such as utilizing co-injection technology, and vibration welding to improve noise abatement performance at a lower cost. Nor have superior sound transmission loss materials been used in air intake manifold shell fabrication.
Accordingly, there remains a need in the art for an air intake manifold having a compact, light-weight construction, improved noise absorption and attenuation characteristics, which operate collectively to reduce engine noise economically, in a highly reliable manner.
The present invention provides an improved air intake manifold shell that provides significantly improved noise reduction at low cost. Materials having superior sound transmission loss properties are combined with a barrier construction especially suited to provide increased absorption, and superior sound transmission loss properties.
In one embodiment, the invention provides a co-injection molded air intake manifold shell comprising an inner and outer layer separated by a sound-absorbing core. Each of the outer layers is composed of a polyamide resin. Preferably, the polyamide resin contains glass-fiber reinforcement and mineral filler such as barium sulfate. The inner layer is composed of a low-density, high damping material having a foam structure, and or dispersed high-density material such as a glass-fiber reinforced and mineral filled polyamide resin.
Optionally, the layers are provided with a plurality of blisters to distribute localized increased core thickness (pockets) at predetermined locations across the air intake manifold shell surface, the locations being selected to increase noise transmission losses. The noise transmission loss is further improved by introducing higher density materials into the localized pockets.
In an alternative embodiment, a double layer air intake manifold shell comprises an inner and outer layer separated by an air core.
In yet another embodiment, a single layer air intake manifold shell is comprised of a polyamide resin containing glass and mineral fillers such as barium sulfate or high damping carbon nano-tubes. Optionally, the single layer air intake manifold shell has non-uniform thickness. The thickness is preferably greatest over preselected areas from which emanate noise transmissions having larger amplitude, to increase noise transmission losses.
The present invention incorporates barrier and absorption technologies in plastic constructions thereby reducing overall noise transmittance while at the same time reducing space, weight and cost requirements of existing technologies.